Epilithic biofilms of the Eastern Caspian (Aktau region, Kazakhstan) under conditions of falling sea level

Abstract

Communities of microorganisms that form biofilms on the rocky shores of the Middle Caspian are capable of maintaining the integrity of the coastal landscape in the conditions of sea retreat associated with the ongoing drop in sea level since 1995. Algal-bacterial biofilms developing on rocky substrates of the East Caspian coast within the City of Aktau were studied in autumn (October 2022) and spring (April 2023) seasons. Communities in biotopes with different structure were investigated. It has been established that the most stable and diverse communities with a pronounced vertical structure live in the areas with high sheer cliffs on capes. On flat areas of the coast, which have undergone recent shallowing and are protected from surfing waves by ridges of large stones, less diverse cenoses, demonstrating clear spatial organization. In the shallow open areas of the shore, which are subject to intense wave action, live communities of two types were observed. Both cenoses contained a relatively small number of species, but differed in structure and potential for protecting the coast from erosion. The first of them live in biotopes outside the impact of urban domestic sewage, and are able to protect coastal marl from destruction due to the development of stable, rapidly regenerating complex structural elements. The latter were noted in the conditions of along-shore spreading of untreated domestic wastewater from new city developments located close to the coast. Such biofilms were no longer able to protect marls from being destroyed by waves, and took the form of constantly renewed patches with minimum diversity of components and unstable spatial organization.